#include <Wire.h>               // deals with I2C connections
#include  <LiquidCrystal_I2C.h>  // activates the LCD I2C library

String menuOption[] = {{"Temperature"},{"Pressure"},{"Gas"},{"Humidity"}};

const int downButtonPin = 5;
const int selectButtonPin = 6;
const int clearButtonPin = 7;

int directionPush = 0;

// BUTTON PRESS STATES FOR EACH FUNCTION, ALL SET TO "LOW".
//  MAKE THESE "BOOLEAN" VARIABLES AS THESE ONLY WILL BE "HIGH" OR "LOW".
boolean buttonStateDown = LOW;
boolean lastButtonStateDown= LOW;
boolean currentButtonStateDown = LOW;
//select an menu option
boolean buttonStateSelect = LOW;
boolean lastButtonStateSelect = LOW;
boolean currentButtonStateSelect = LOW;
//clear button, will reset the menu back to the start
boolean buttonStateClear = LOW;
boolean lastButtonStateClear = LOW;
boolean currentButtonStateClear = LOW;

// DEBOUNCE VARIABLES TO MEASURE THE DEBOUNCING TIME OF A BUTTON PUSH.
//  MAKE THESE "UNSIGNED LONG" VARIABLES AS THE NUMERICAL VALUE WILL HAVE AN EXTENDED  SIZE.
unsigned long lastDebounceTime = 0; //takes snapshot of time when button is pressed
unsigned long debounceDelay = 50; //delay time in milliseconds

//setup the lcd, whatever is connected to the arduino
LiquidCrystal_I2C  lcd(0x27, 16, 2);   // Activates the LCD "object"

void setup() {
  //setup the lcd, turn on and clear
  lcd.backlight();                  // THESE COMMANDS TURN ON AND  CLEAR THE LCD SCREEN
  lcd.init();
  lcd.clear();

  //set button pins as inputs
  pinMode(downButtonPin, INPUT);
  pinMode(selectButtonPin, INPUT);
  pinMode(clearButtonPin, INPUT);

  delay(1000);
}

void loop() {
  //again set up lcd and serial monitor
  //create an arrow system
  lcd.setCursor(0,0);                           // Menu displayed  on the LCD.
  lcd.print(menuOption[directionPush]);         // The menuOption  that is displayed is determined by the left or right push.  

  //wait for an input
  currentButtonStateDown = digitalRead(downButtonPin);
  currentButtonStateSelect = digitalRead(selectButtonPin);
  currentButtonStateClear = digitalRead(clearButtonPin);

   if (currentButtonStateDown  != lastButtonStateDown || currentButtonStateSelect != lastButtonStateSelect || 
  currentButtonStateClear != lastButtonStateClear)        
  // If there is  a button push on any of the buttons, the following routine runs to check if it was  a valid press:
  {
  lastDebounceTime = millis();      // lastDebounceTime  is set equal to the running millis() function.
  }  

  if ((millis()-lastDebounceTime) > debounceDelay)
 /* If the lastDebounceTime (aka. the  "snapshot" time) minus the running millis() function is higher than the set debounce  delay, the following routine
 below runs and checks which button was pushed:*/  
  {
    //down button press
    if (currentButtonStateDown != buttonStateDown)
    {
      buttonStateDown = currentButtonStateDown;

      if (buttonStateDown == LOW )
      {
        directionPush++; //for ours will have arrow go down the list
      }
        if (directionPush > 4) //resets menu, goes back to top of list
        {
          directionPush = 0;
        }
      lcd.clear();
    }
    //select button press
    if (currentButtonStateSelect != buttonStateSelect)
    {
      buttonStateSelect = currentButtonStateSelect;

      if (buttonStateSelect == LOW && directionPush == 0)
      {
        //clear lcd, set cursor
        //print the option
        lcd.clear();
        lcd.setCursor(0,0);  
        lcd.print("Temperature");
        lcd.setCursor(0,1);
        lcd.print("IS  ENTERED");
        delay(2000); 
      }

      if (buttonStateSelect == LOW && directionPush == 1)
      {
        //clear lcd, set cursor
        //print the option
        Serial.println("82 Pressure");
        lcd.clear();
        lcd.setCursor(0,0);  
        lcd.print("Pressure");
        lcd.setCursor(0,1);
        lcd.print("IS  ENTERED");
        delay(2000); 
      }

      if (buttonStateSelect == LOW && directionPush == 2)
      {
        //clear lcd, set cursor
        //print the option
        Serial.println("92 Gas");
        lcd.clear();
        lcd.setCursor(0,0);  
        lcd.print("Gas");
        lcd.setCursor(0,1);
        lcd.print("IS  ENTERED"); 
        delay(2000);
      }

      if (buttonStateSelect == LOW && directionPush == 3)
      {
        //clear lcd, set cursor
        //print the option
        Serial.println("62 Humidity");
        lcd.clear();
        lcd.setCursor(0,0);  
        lcd.print("Humidity");
        lcd.setCursor(0,1);
        lcd.print("IS  ENTERED"); 
        delay(2000);
      }
      //clear the lcd
      lcd.clear();
    }

        // CLEAR BUTTON PRESS
    if (currentButtonStateClear !=  buttonStateClear)        
    { 
    buttonStateClear = currentButtonStateClear;  

      if (buttonStateClear == LOW) 
      {
        //clear lcd, set the cursor
        lcd.clear();                                          // The press counts for both the up and  down variables are also reset to zero.
        lcd.setCursor(0,0); 
        lcd.print("MENU");
        lcd.setCursor(0,1);
        lcd.print("IS CLEARED");
        delay(2000);
      }
    lcd.clear();
  }
  }
    // After a button is pushed and the count recorded,  all the states reset back to LOW for the data to be processed correctly.
  lastButtonStateDown  = currentButtonStateDown;       // resets the down button state to LOW
  lastButtonStateSelect  = currentButtonStateSelect;     // resets the enter button state to LOW
  lastButtonStateClear  = currentButtonStateClear;     // resets the clear button state to LOW
}